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How to Open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 12:31 AM

I have to open two manholes on a Ball Mill Shell (6 m dia x 9 m length).

Please, Could you tell me your points of view or opinions how to open it. I think that, before to open the manholes I have to install inside trusses in order to avoid the shell deformation, because it is an old ball mill, and it is possible to find fatigue stress. Other point to take in to account is, If I need to get out the balls charge or it can be avoid putting a pair of supports on the shell.

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 9:41 AM

Has this ball mill been inactive for a long period? I ask that because these mills can sag and this can pinch the bolts to the point they become oblong and break on attempted extraction. In this case they will need drilling with careful concentricity to avoid the thread and re-tapped to a larger round size after corrective work to correct the sag (at time, this damage can ruin a mill left for a decade or so)

If not sagged, you might try repeated thermal cycling with a torch followed by a oil quench (blast off the oil with a pressure washer before the next torch session. This can often degrade the corrosion mediated bond caused by the inexorable expansion of the rust in the threads. Often stainless bolts are used, but the steel shell will rust and the grip is strong enough to exceed the bolt strength.

In any event, call in an experienced ball millwright, they have the tools and experience to deal with this. Once you have observed the process, you will gain some experience and might be able to do it yourself.